The present invention relates generally to an improved vascular graft system, and in particular to a stented vascular graft system incorporating improved stents and grafts designed to provide flow transfer from an aortic source to a branch flow path for coronary bypass procedures. In accordance with the present invention, graft material is appropriately secured to the stent structure so as to facilitate this step in the coupling of the graft system to the vasculature of the patient, thereby expediting the surgical procedure while at the same time reducing the number of suturing steps necessary in the procedure. The features of the present invention are set forth in greater detail hereinafter.
Coronary bypass surgery has become a common procedure, and is normally indicated for conditions requiring replacement and/or reconfiguration due to blockage of the coronary blood flow within a patient. Apparatus and techniques are also disclosed herein for selectively monitoring the flow through a graft. The present invention involves use of a stented graft, and particularly wherein the stent is utilized to receive the graft and also for modifying the flow pattern through coupling to relevant portions of the vasculature. Two forms of stented grafts are utilized in a typical surgical procedure, with a first form being employed for introduction into a coronary artery downstream from a blockage site, and with the second form of stented graft being employed to couple the distal end of the graft network to a point of relatively lower flow pressure, and to serve as a terminus for the grafted structure. In the second form of stented graft, means are provided for suturing the stent to a selected location, typically at the right atrium or superior vena cava. The utilization of stented grafts facilitates and expedites the procedure while reducing the number of necessary steps, all of this being achieved without compromising the efficacy of the overall procedure.
In a typical bypass procedure, a section of the vascular system in a patient's body that has become impaired or inoperative through disease or other defect may be treated so as to improve flow to those portions previously being given an inadequate or limited supply of blood. In order to create the graft network, biocompatible graft material may be employed, such as, for example, Gortex.TM., with this being a polytetrafluoroethylene-based material normally being accepted by the patient's body. Thus, such graft material is frequently and typically utilized in bypass as well as in other procedures such as, for example, as a joint reinforcing material, such as a brace interposed across the knee.
Because of the physical properties of the biocompatible graft material, stent suturing, while possible, is frequently difficult to complete. The procedure is one which requires great dexterity, and when done at the site, is frequently in a zone with limited accessibility. In the design of the stent portion of the stented grafts, a certain degree of axial offset is provided in order to more fully and completely expose a portion of the stent to which a graft must be applied during the surgical procedure. Because of this greater accessibility and visibility, the stented graft device of the present invention is highly desirable.
Coronary bypass procedures are frequently undertaken with patients whose coronary arteries have been partially or almost completely blocked, thereby impeding and disrupting the proper flow of blood through the vascular system. While bypass procedures have been undertaken for some period of time, one meticulous and time consuming step is that of suturing the vascular graft elements. The time required for completing each such suture is reduced significantly through providing a pre-attached or stented graft in accordance with the present invention.
As a further feature of the present invention, means can be provided in combination with the vascular assembly for monitoring blood flow through various branches of the graft configuration. In particular, flow rate monitoring may be achieved through utilization of devices functioning in response to temperature variations resulting by introducing a temperature energy signal into the bloodstream, and measuring and/or detecting the thermal response at a downstream location. Another technique suitable for use in connection with the present invention is based upon the use of ultrasonic signals, wherein the system comprises one or more signal generators in communication with the blood flow (transducers) along with detection means, normally an array transducer exposed to the signal. Doppler techniques may be employed to determine flow rate and volume. Such systems are known in the art, with a thermal response system being disclosed in U.S. Pat. No. 5,989,192, and with ultrasonic systems being disclosed in U.S. Pat. No. 5,967,989; 5,807,258 and 5,588,436.
In order to evaluate the condition of an individual graft, determinations of flow velocity and overall blood volume provide a good indicator. A determination of pressure differentials between opposed ends of a graft will provide valuable information as well. Obviously, as deposits collect along the interior wall of a graft, pressure differentials will increase along with a corresponding decrease in velocity and flow volume. The utilization of the stented grafts in accordance with the present invention reduces some of the potential for buildup within certain other graft structures, this being accomplished by tailoring the configuration of the flow channel through the stent so as to preserve flow patterns, and also preserve and/or reduce the tendency for any increase in the Reynold's number within the blood flow through the graft network.